1. Field of the Invention
The present invention relates to an intake system in a V-type 4-stroke engine for an outboard engine system, which includes a crankshaft disposed vertically, and heads of left and right banks disposed to face rearwards, and which is covered with an engine hood, and particularly to an intake system in an engine for an outboard engine system, which is designed so that an air-charging characteristic can be changed in accordance with the operational state of the engine to maintain a high power output performance in a wide operation range from a low speed to a high speed.
2. Description of the Related Art
There is an intake system in an engine for an outboard engine system, which is known, for example, from Japanese Patent Application Laid-open No.10-61446 and in which the effective length of an intake line is changed over in accordance with the operational state of the engine to satisfy the power output performance in a wide operation range.
However, in the system disclosed in the above Patent Publication, an intake pipe extending in a longitudinal direction is disposed on one side in a lateral direction of the engine. Therefore, an engine hood including the intake pipe and covering the engine is necessarily increased in width, inevitably resulting in an increase in size of the engine hood. This tendency is significant particularly when such intake system is applied to a V-type 4-stroke engine.
The present invention has been achieved with the above circumstances in view, and it is an object of the present invention to provide an intake system for a V-type 4-stroke engine for an outboard engine system, wherein the air-charging characteristic is changed in accordance with the operational state of the engine to maintain a high power output performance in a wide operation range of from a low speed to a high speed, while avoiding an increase in size of the engine hood.
To achieve the above object, according to a first aspect and feature of the present invention, there is provided an intake system in a V-type 4-stroke engine for an outboard engine system, the engine including a crankshaft disposed vertically, and cylinder heads of left and right banks disposed to face rearwards, and an engine hood covering the engine. The intake system comprises an intake air inlet which is provided in an upper portion of a longitudinally flat intake air dispensing box disposed between the cylinder heads and a rear wall of the engine hood and which leads to an intake passageway in a throttle body, the inside of the intake air dispensing box being divided by a partition wall into first and second dispensing chambers each communicating with the intake air inlet and extending longitudinally; and an on-off valve mounted on the partition wall and capable of bringing the first and second dispensing chambers into and out of communication with each other. Each of the left and right banks has an intake port which communicates with the first and second dispensing chambers.
With the first feature, a two-line resonant supercharging intake system, which comprises an intake line extending from the first dispensing chamber to the intake port in the left bank and an intake line extending from the second dispensing chamber to the intake port in the right bank, and in which no charging interference of the lines with each other is produced, is constituted by closing the on-off valve in a low-speed operation range of the engine to bring the first and second dispensing chambers out of communication with each other. The peculiar vibration of the two-line resonant supercharging intake system is set to be substantially equal to an opening/closing cycle of the intake valve in the low-speed operation range of the engine, whereby a resonant supercharging effect can be effectively exhibited to increase the intake air charging efficiency in the low-speed operation range of the engine to enhance the power output performance.
A single surge tank having a large capacity is constituted by opening the on-off valve in a high-speed operation range of the engine to bring the first and second dispensing chambers into a large communication with each other. Thus, the peculiar frequency of the resonant intake system is increased to correspond to the opening/closing cycle of the intake valve in each of the banks in the high-speed operation range of the engine, whereby the resonant supercharging effect can be exhibited to increase the intake air charging efficiency in the high-speed operation range of the engine to enhance the power output performance.
Moreover, the longitudinally flat intake air dispensing box is disposed in proximity to the heads of the left and right banks and hence, the intake air dispensing box can be disposed in a narrow space between the engine and the rear wall of the engine hood. Thus, it is possible to provide an improvement in space utilization efficiency in the engine room and to suppress an increase in size of the engine hood.
According to a second aspect and feature of the present invention, in addition to the first feature, an opening is provided in one sidewall of the intake air dispensing box; a lid plate having the partition wall is secured to the intake air dispensing box to close the opening; and the on-off valve is mounted to the partition wall of the lid plate.
With the second feature, the intake air dispensing box provided with the on-off valve can be assembled with a good efficiency by constructing an assembly of the lid plate and the on-off valve and then securing the lid plate to the intake air dispensing box.
According to a third aspect and feature of the present invention, in addition to the first or second feature, the intake air dispensing box having the intake air inlet is formed of a synthetic resin, and a plurality of intake branches made of a synthetic resin and leading at their downstream ends to a plurality of intake ports in the engine are connected to the sidewall of the intake air dispensing box, funnels are formed at the upstream ends of the intake branches and disposed within the intake air dispensing box, thereby constructing an intake manifold. The intake air dispensing box is comprised of a first box half and a second box half welded to each other on one plane, the intake air inlet being provided in one of the box halves. Plurality of the intake branches are comprised of a plurality of intake branch bodies integrally formed on the first box half and each having a portion of each of the funnels, and a plurality of funnel segments welded to said intake branch bodies on one plane in the intake air dispensing box and each constituting the remaining portion of each of the funnels.
With the third feature, the formation of each of the components of the intake manifold can be facilitated, and when the components are welded together, the pressing force on all the weld surfaces is equalized reliably, thereby equalizing the weld margin and providing the stabilization of the weld strength. Thus, it is possible to improve productivity and quality of the intake manifold.
According to a fourth aspect and feature of the present invention, in addition to the third feature, a connector is integrally formed on the plurality of funnel segments and connects the funnel segments together.
With the fourth feature, it is possible to form the plurality of funnel segments along with the connector at a stroke and to easily conduct the vibration welding of them to the intake branch bodies.
According to a fifth aspect and feature of the present invention, in addition to the third feature, a plane on which the first and second box halves are welded to each other and a plane on which the intake branch bodies and the funnel segments are welded to each other, are disposed on one plane.
With the fifth feature, it is possible to further enhance the productivity of the intake manifold.
The above and other objects, features and advantages of the invention will become apparent from the following description of the preferred embodiment taken in conjunction with the accompanying drawings.